Transfer method for silver salt diffusion and liquid agent for use in this method



United States Patent Int. Cl. Gll3c 5/54 US. Cl. 96-29 6 Claims ABSTRACT OF THE DISCLOSURE A method for transferring a silver salt diffusion, using a negative material, on the silver halide emulsion layer of which an image is exposed and which is subequently wetted with a fluid causing it to be developed, and subjected to compression together with a receiving or transfer material, wetted with another liquid, wherein the said other liquid contains, in addition to nuclei-forming substances and a silver salt solvent, also substances known to act as reducing agents in photographic developers or photographic layers and/or containing organic acids capable of acting as reducing agents and/or improving the durability of the solution and of stabilizing the picture.

The invention relates to a silver salt diffusion transfer method making use of a negative material, having a silver halide emulsion layer on which an image is formed by exposure, and a receiving material, to which the image is transferred, wherein the exposed negative material is moistened with a liquid effecting the development and is subjected to compression together with the moistened receiving material, which is made of paper, felt or textile material, the receiving material being wetted with another liquid.

The invention also relates to the composition of said other liquid.

The German Pat. No. 764,572 describes the so-called silver salt diffusion method and states that widely varying substances may be used as receiving materials, such as, for example, uncoated papers, textile sheets, wood, celluloid and other plastics and the like materials. In this conjunction it should be stated that the term material relates to foliate materials. It is also apparent from the said patent specification that the transfer may be aided by the presence of substances supportingthe diffusion process. The diffusing or diffused silver halide can be developed image-wise without exposure, the development being supported by added nuclei or substances forming reducing nuclei. The developed picture may be produced, for example, on a baryta paper or on a textile base which has been wetted in the same bath as the silver halide material. In the practical application of this method, such as it has been developed commercially in conjunction with foliate copying materials, a separate positive or receiving-layer has been provided which contains the reducing nuclei or the said substances. This layer is usually arranged on a special carrier so that the layer and the carrier form together the receiving material.

It is also known to use this receiving layer independently of a carrier and to apply it, for example, as covering layer to the negative layer. An arrangement of this kind has been described in German Pat. No. 1,171,740 where it has been designated as a colloidal covering and receiving layer. This layer need not contain any reducing nuclei, but, according to the mentioned specification, reducing nuclei are added to the colloidal receiving layer 3,510,302 Patented May 5, 1970 by way of the liquid treatment agent. According to this patent, suitable nuclei-formers are sulphides, selenides, polysulphides, polyselenides, thiourea, mercaptans, stannous halides, heavy metals or their salts, fogged silver halide, sulphides of heavy metals such as antimony, bismuth, cadmium, cobalt, lead, nickel and silver. Amongst these, the heavy metals, for example, silver, gold, platinum, palladium, and mercury, preferably in colloidal form, and the noble metals, are regarded as the most efficient.

In the method according to patent specification 1,171,- 740, the image-receiving layer is thus provided as a cover layer on the negative, and a sheet of material is provided for receiving the image developed in the cover layer. Since according to patent specification 764,572 the difficulty soluble silver compound or colloidal silver, which is produced in the receiving layer, is non-diffusable, the colloidal cover or image-receiving layer containing the developed image is also transferred during the transfer to the receiving sheet, paper or the like.

With other copying methods it has already become possible to transfer a usable picture to an ordinary sheet of paper without using a positive layer. However, this is a physical method, such as for example, a photo-electric method.

The German Pat. Nos. 764,572 and 1,171,740 are based on the use of reducing nuclei, such as used, for example, in the silver salt diffusion method generally known as the Copyrapid method.

If the reduction nuclei according to patent specification 1,171,740 are provided in the processing liquid, which not only serves for carrying out the developing, but also for the complex salt formation of the unexposed and undeveloped silver halide, then the same limitations exist, in respect to the stability of such solutions, as are known to exist in developers used in the silver salt diffusion method. These limitations are due to the simultaneous presence of air oxidation products, used and unused developing substances, the rising content of silver halide solvents caused by the increased number of copies and silver halide complex compounds which diffuse into the solution and may be active as reduction nuclei.

A method has already been proposed which operates on the basic of the silver salt diffusion method, and which makes possible the economical production of a picture on an uncoated carrier. In this conjunction, the term uncoated means that the carrier does not contain any filmforming colloids, but does not exclude the wetting with a liquid of the kind referred to hereinbefore as the other deliquid. Preferably, the receiving material is processed in the moist state produced by the wetting. It has also been proposed that the said other liquid should containing reducing nuclei or substances forming reducing nucleifi as well as a silver salt solvent, or that these substances should be present in a aqueous solution.

The liquid for the development of the exposed negative in the method is an activator known per se in the development of commercially used negative materials.

The proposed prior art method has the advantage of using simple and cheap materials, while eliminating the problem of coating, particularly the application of a coating of the receiving material on a carrier. Additional advantages are that the materials can be stored for prolonged periods and are not influenced by fluctuations in the air moisture and temperature. Generally, the durability and usefulness of the used liquids are significantly improved because mutually reacting substances may be provided in different baths. For example, in the proposed method, alkali is supplied from the liquid developer for the exposed negative solely by contact between the wetted negative and the receiving material wetted with the other liquid, so that there is a low proportion of alkali. Alkali 3 residues which remain in the copy are known to cause yellowing of the produced picture.

According to a preferred embodiment of the proposed, prior art method, the liquid agent for the receiving material is an aqueous solution of nuclei-forming substances and sodium thiosulphate, as well as wetting agent (Mirasol). A preferred nuclei-former is a platinum solution, and conveniently a solution containing a concentration of about 0.02% of a hexachloroplatinum(IV)acid and/ a gold(III)chloride-hydrochloric acid is used in the liquid for the receiving material.

The already proposed method provides a new solution for carrying out the silver salt diffusion method on an uncoated carrier. Hitherto this has not been possible in a comparable manner from a practical point of view so that always a separate positive and receiving layer was provided which in most cases contained the reducing nuclei. The receiving layer may be arranged on a special carrier or as covering layer on the negative. However, it is always necessary to use a liquid chemical agent, serving not only for carrying out the developing, but also for the complex salt formation of the unexposed and undeveloped silver halide. This has the disadvantages that solutions of this type are not very durable, because air oxidation products, used and unused developer substances and a content of silver halide solvent caused by a higher number of copies, have an adverse effect.

Hitherto known and commercially available materials have the further drawbacks already mentioned, and relating to the storage of a copy after the processing, because due to the treatment with an alkaline liquid developer, alkaline residues remain in the copy, causing its stability to be reduced and the copy to become yellow. With known, commercially available, so-called dry substances, the silver picture adhere's less well to the picture receiving carrier, so that the picture may be lost under moist and warm storing conditions. Also these so-called dry materials operate with a chemical liquid developer which acts on the negative and on the receiving material and which contains, therefore, the substances necessary for the developing.

For the clearer understanding of the invention, it should be stated that the term reducing nuclei means hereinafter noble metal in colloidal form; while substances forming reducing nuclei are metals which are not amongst the noble metals, such as, for example, zinc, copper and cobalt. However, substances acting as reducing agents are substances which reduce silver halide to metallic silver, that is to say, chemically active substances which are not present in the form of nuclei or capable of forming nuclei, but which contribute to the production of a black picture by chemical action.

The present invention has the object of improving the method already proposed, both by improving the quality of the copies with regard to the blackening and to their durability, and with regard to the durability and usability of the said other liquid for the receiving material, in the case a larger number of copies is to :be produced.

According to the invention, this object is realized in that the said other liquid contains, in addition to nucleiforming substances and a silver salt solvent, also substances which are known as reducing agents in photographic developers or photographic layers and/ or organic acids which can act as reducing agents and/or improve the durability and which stabilize the produced picture.

The' efiect produced according to the invention can be explained in that the addition of organic acids improves 4 be transferred during contact with the negative material, is neutralized after the production of the copy.

Furthermore, hitherto the reducing nuclei-containing liquid, that is to say, in conventional methods also the ordinary liquid developer, could be prematurely reduced, upon the occurrence of certain phenomenon, or where such liquid had been stored for prolonged periods. Also here, the organic acids have a stabilizing effect.

The reducing agents assist in the production of the picture with regard to the blackening and also with regard to the speed of operation. Both these eflects represent a substantial improvement of the already proposed method.

According to the invention, the reducing agent and the organic acids may be used together or separately. A generally uniform effect is achieved in that there is added to the liquid for the receiving material a substance which acts both as an acid in the sense hereinbefore outlined,

and as a photographi-cally effective reducing agent. Such a substance is, for example, ascorbic acid. The use of such substances, which not only act as stabilizers with regard to the alkali and the reducing nuclei, but which also reduce silver to metallic silver, shows that, according to the main feature of the invention, only a single substance need be added, in order to produce all the effects hereinbe'fore described.

The organic acids used are, for example, acetic acid, citric acid, salicylic acid, phthalic acid and acids of corresponding effect.

Suitable reducing agents are, in addition to the ascorbic acid already mentioned, substances used in photography as developers, such as, for example, hydroquinone, methyl-p-amino-phenolsulphate, aminophenol and derivatives of aminophenol, pyrocate'chol, l-phenyl-3-pyrazolidon, and derivatives of 3-pyrazolidon, hydroxylamin hydrochloride and substances with similar action.

According to the invention, the said additives neutralize residual alkali in the receiving material and achieve a particularly good picture stability even under adverse conditions. This also results from the fact that the pictureformingsubstances in the receiving material, namely the complex undeveloped silver halide, are concentrated in a state which is largely insenstive to moisture, while the substances in the liquid for the receiving material ensure, by virtue of the complete surface wetting, that subsequently reacting substances are transformed on the surface into a stable compound.

According to the already proposed method, the negative material may be commercially available Copyrapid-Dry- Negative paper, and the developer may be an activator designed therefor. When ordinary negative diifusion papers are used, a known, commercial developer for these papers can be used.

Although it has already been proposed to use for the receiving material a solution with a concentration of only about 0.02% of a hexachloroplatinum(IV)acid or a gold (III)chloridehydrochloric acid, and to produce substantial advantages by these means, it has been shown that the addition of the substances mentioned to the solution, according to the invention, produces a substantial improvement.

In the following, the former solution is designated as a 0.02% platinum solution as and the latter solution a gold solution with a 1% concentration.

A particularly good result is obtaned if the said other solution for treating the receiving material has the following initial or starting composition.

Naturally, with an increased addition of either the gold solution or the platinum solution, one or the other solution may be omitted. The references in the following examples to starting solution refer to the above composition; however, as already stated, it is also possible to work only with a gold solution or only with a platinum solution, and to add the additives of the invention to the respective starting solution. Optimum results are achieved with the starting solution mentioned above and with the following additives for forming the liquid for treating the receiving material.

In a further example the following total composition is recommended Example 7 H O1000 ml. Mirsasol15 ml. Gold solutionml. N2S2O31 ml. Ascorbic acid--O.1 g.

Apart from what has been stated hereinbefore, the advantages are also apparent from transparency measurements of copies made in the various solutions under otherwise identical conditions. The measurements were carried out after a bath utilization of 100 copies at size DIN A 4 (11%" x 3%.") per liter of solution. If this measurement of the transparency is made with materials which have been processed either only with the starting solution, or with the enriched solution in accordance with the invention, the following values are obtained:

Picture Bas I Designation surfaces surfaces Drfierence Starting solution 1. 15 0. 65 0. 50 Example 1 1. 95 82 1. 13 Example 2 1.70 0.66 1.04 Example 3 1. 60 0.66 0. 94

It may be readily seen that the contrast is substantially improved, and that improvement is, in the case of Examples 1 and 2, above 100%.

It is also clear from the examples that, calculated on starting quantity of 1000 ml. H O, the additions to the starting solution are of the order of up to 0.6 gram. More particularly, in the case of the organic acids, the addition is preferably of the order of magnitude up to 0.5 gram, calculated on a starting charge of 1000 ml. H 0.

We claim:

1. In a silver salt difiusion transfer method, wherein an image is formed by exposure on the silver halide emulsion layer of a negative sheet and the thus exposed negative sheet is developed by a developer liquid, whereupon the developed image is transferred by pressure contact to a receiving sheet, the improvement which c0m prises that the receiving sheet is uncoated sheet material which, immediately prior to the pressure contact with the negative material is moistened with a liquid of dif ferent composition than said developer liquid, said liquid comprising an aqueous solution containing (a) a silver salt solvent,

(b) hexachloroplatinic (IV) acid and/or gold (III) chloride hydrochloride, and

(c) at least one compound being acetic acid, citric acid, salicylic acid, phthalic acid, ascorbic acid, hydroquinone, methyl-p-aminophenol-sulfate, aminophenol-sulfate, aminophenol, an aminophenol derivative, pyrocatechol, 1-phenyl-3-pyrazolidone, a derivative of 3-pyrazolidone or hydroxylemine hydrochloride.

2. The improvement of claim 1, wherein the compound of (c) is ascorbic acid.

3. The improvement of claim 1 wherein up to about 0.5 g. of said compound (c) per milliliter of water are contained in said liquid of different composition.

4. The improvement of claim 1, wherein up to about 0.6 g. of said compound (e) per 1000 ml. of water are contained in said liquid of different composition.

5. A liquid for use in silver salt diffusion transfer methods for wetting the uncoated receiving sheets to which the exposed and developed picture is transferred, said liquid comprising an aqueous solution of (a) hexachloroplatinum (VI) acid or gold (III) chloride hydrochloric acid.

N32520:; and

(c) at least one of ascorbic acid, acetic acid, citric acid, salicylic acid, phthalic acid, hydroquinone, methyl-p-aminophenol-sulfate, aminophenol, an aminophenol derivative, pyrocatechol, 1-phenyl-3-pyrazolidone, a derivative of 3-pyrazolidone or hydroxylamine hydrochloride.

6. A liquid as claimed in claim 5, wherein (c) is about 0.5 g. of ascorbic per 1000 ml. of water.

References Cited UNITED STATES PATENTS 2,352,014 6/1945 Rott 9629 2,740,717 4/1956 Mutegy et al. 9629 3,179,517 4/ 1966- Fregillus et al 9629 2,644,756 7/1953 Land 9629 FOREIGN PATENTS 764,572 1952 Germany.

GEORGE F. LESMES, Primary Examiner J. P. BRAMMER, Assistant Examiner 

